With the rapid development of the power electronic technology, the application of the power electronic devices is more and more extensive. Wherein, the inverter is used widely in the application occasions, such as uninterruptible power supply (UPS), active power filter (APF), static var generator (SVG), and the like. In the art, various attempts and efforts have been made aiming at improving the respective specifications, such as decreasing the volume of the inverter, improving the efficiency of the inverter, reducing the cost of the inverter, decreasing the output harmonics of the inverter, increasing the applicability of the inverter, in various occasions, however, various circuit topologies have their respective limitations, and the respective problems cannot be solved excellently.
The prior inverter topology is shown mainly in FIG. 1˜FIG. 2. Wherein FIG. 1 shows a normally used 3p4w structure of two-level inverter, in which the neutral line is connected directly with the midpoint of a bus capacitor. Conversely, if the neutral line is not connected with N, then it will be a 3p3w structure. The three phases can be decoupled completely because of the existence of the neutral line, and also can be controlled individually. However, the neutral line current flows through the bus capacitor, and it is required to design a large bus capacitor in order to suppress the ripple current. If it is a 3p3w structure and a specific order of harmonic current is required to be outputted, such as the second harmonic current, similarly, it is necessary to design a large capacitor to conform to the life requirement of the direct current capacitor. FIG. 2 shows a 3p4w structure of three-level inverter. Similarly, the neutral line is connected with the midpoint of a bus capacitor, if it is not connected, then it will be a 3p3w structure. In 3p4w structure, the neutral line current flows through the bus capacitor, and it is required to design a large bus capacitor in order to suppress the ripple current. If it is a 3p3w structure and a specific order of harmonic current is required to be outputted, such as the second harmonic current, similarly, it is necessary to design a large capacitor to conform to the life requirement of the direct current capacitor
In different application occasions, if neutral line current and specific order current are not necessary to be outputted, then only smaller direct current bus capacitor will conform to the life requirement. While in some specific application occasions, large neutral line current or specific order harmonic current are required, then larger direct current bus capacitor is required to conform to the life requirement of the capacitor. For the versatility of the product, normally, the capacitor is designed to be larger, however, in the normal application occasions, it causes a waste of the capacity of the direct current capacitor.
In view of this, a subject to be solved in the art by the related technicians is how to design a novel inverter, wherein one of the problems of the versatility of the capacitor design has been solved and it can be applied to various occasions.